Respiratory gases.

Respiratory gases have access to the human circulation by diffusing through alveolar walls into pulmonary capillaries. Because of this circulatory access, these gases can act like other types of drugs, and can produce effects both locally in the lungs and systemically in distant organs or tissues. This article reviews the metabolism, pharmacology, and therapeutic use of the three most common gases used in the practice of respiratory medicine: oxygen, carbon dioxide, and helium.